The present invention relates generally to indexable cutting inserts and cutting tools including such indexable cutting inserts and, more particularly, to indexable cutting inserts and cutting tools including such indexable cutting inserts that prevent improper mounting of the cutting inserts on a toolholder.
In designing cutting inserts, it is typically desirable to provide the cutting insert with the maximum number of usable cutting edges possible so that the insert can be indexed to different positions to permit use of a new cutting edge when an edge is worn or broken. Inserts are typically mounted to toolholders by means such as clamping screws or bolts, and many current designs permit an insert to be indexed by turning the insert around the bolt so that a fresh cutting edge is moved to a working or active position. In addition, many current designs are of “double-sided” inserts that permit the insert to be flipped over so that the insert can be indexed around the screw or bolt, such as is shown in U.S. Pat. No. 7,241,082.
When making smaller inserts intended to be used to machine smaller items or shapes, it becomes increasingly difficult to make indexable inserts without compromising the strength of the insert or the ability to provide sufficient surface space on the insert for mounting of the insert against abutment surfaces on a toolholder. It is necessary to provide a hole through the insert for the mounting screw or bolt and, particularly in the case of double-sided cutting inserts, as insert size becomes smaller, a trade-off must often be made between providing a smaller, more fragile screw or bolt or a more fragile insert that has only minimal insert material between the hole and working surfaces of the insert.
A tangentially mounted cutting insert is disclosed in DE 29907623 U1.
U.S. application Ser. No. 14/569,960, filed entitled REINFORCED DOUBLE-SIDED CUTTING INSERT AND CUTTING TOOL WITH REINFORCED DOUBLE-SIDED CUTTING INSERT, which is incorporated by reference, provides one solution to the problem of providing a hole of sufficient size in a small cutting insert without unduly compromising the strength of the insert by providing a cutting insert 225 having the general shape as shown in FIG. 7 for mounting in a toolholder 23 of the general type shown in FIGS. 3-6. A hole 251 extends through a peripheral side surface 247 of the cutting insert 225 from one major side surface 249 to an identical opposing major side surface. The cutting insert 225 also includes two identical supporting end surfaces 241 and two identical minor side surfaces 253. Each minor side surface 253 includes two planar but typically non-coplanar supporting surface portions 255. The four supporting surface portions 255 correspond to four respective cutting edges 263, two cutting edges being formed at the intersection of one of the supporting end surfaces 241 and the peripheral side surface 247 and two cutting edges being formed at the intersection of the other one of the supporting end surfaces and the peripheral side surface. The cutting insert 225 is seated in a pocket 27 of the toolholder 23 so that one of the major side surfaces 249 abuts a major side surface abutting surface 29 of the pocket, one of the supporting end surfaces 241 abuts a central supporting surface portion abutting surface 31 of the pocket, and one of the supporting surface portions 255 abuts a minor side surface abutting surface 33 of the pocket. In this position, the hole 251 aligns with an internally threaded hole 57 in the toolholder 23 and the cutting insert 225 can be clamped relative to the toolholder 23 by a screw in a conventional fashion (see, e.g., FIG. 1). The cutting insert 225 can be indexed in the pocket 27 to four different positions to expose the four cutting edges 263 to a workpiece by rotating the insert 180° about an axis through the hole 251, and by turning the insert 180° without rotating the insert about the axis through the hole. Because the hole 251 through the insert is formed through the major side surface, which is a surface of the insert having a large area relative to, e.g., the supporting end surface or the minor side surface, the hole can be larger than if the hole extended through either the supporting end surface or the minor side surface.
The solution offered by U.S. application Ser. No. 14/569,960 is well suited for small inserts with relatively small corner radii at the cutting edges and corners of the cutting insert by the cutting edges. The inventors have recognized that, as the corner radii become larger, the area available to form the supporting surface portions 255 becomes smaller and once a curved portion of the cutting edge or the corners of the cutting insert extend to one half of the width of the cutting insert measured between the major side surfaces along the axis of the insert, there is effectively no area that can form a planar supporting surface on the minor side surface. The applicants have recognized that, when it is desired to provide an insert with a large corner radius R (see FIG. 14) that diminishes the size of the minor side surface and the supporting surface portions, it may be desirable or necessary that the insert be a single-sided insert. A “large” radius is intended to refer to inserts having corner radii or cutting edge radii that extend over at least a quarter of a width of the insert and, more typically, over more than one half of the width of the insert. The applicants have further recognized that it is desirable to structure such an insert so that the insert cannot be improperly mounted with insufficient support along the minor side surface of the insert.
Accordingly, it is desirable to provide a cutting insert with means for preventing improper mounting of the insert, and a cutting tool including such an insert.
In accordance with an aspect of the present invention, a cutting insert comprises a rake end surface having four corners and, in a center thereof, a central surface portion, a supporting end surface having four corners and, in a center thereof, a central supporting surface portion, a peripheral side surface extending between the rake end surface and the supporting end surface, the peripheral side surface comprising two opposing major side surfaces, a hole extending through the cutting insert from one of the major side surfaces to the other of the major side surfaces, and wherein the central surface portion is disposed at a greater distance from a central axis of the hole than is the central supporting surface portions. The single-sided cutting insert has a corner radii or cutting edge radii that extend over at least a quarter of a width of the cutting insert.
In accordance with another aspect of the present invention, a cutting tool comprises a toolholder, the toolholder comprising a cutting insert receiving pocket, the cutting insert receiving pocket comprising a major side surface abutting surface and a central supporting surface portion abutting surface, and a cutting insert as set forth above, wherein one of the two major side surfaces of the cutting insert abuts the major side surface abutting surface and the central supporting surface portion abuts the central supporting surface portion abutting surface when the cutting insert is received in the cutting insert receiving pocket.
Each figure in the drawings is drawn to scale. However, sizes of cutting inserts maybe reduced or enlarged by a certain amount.